Some semiconductor devices such as a metal-oxide-semiconductor field-effect-transistor (MOSFET) include freewheeling diodes. For example, Patent Documents 1 to 3 each propose a structure of including a Schottky barrier diode (SBD) in a MOSFET unit to be applied as a freewheeling diode. Moreover, a structure of placing a low-resistance layer in a well with a large area is proposed as a structure for increasing reliability in high-speed switching in a SiC-MOS structure as described in Patent Document 4.